Amalgam materials for filling a prepared tooth cavity are well known in dentistry, and are formulated by vigorous mixing or triturating of mercury and a powder or pellet of silver or silver alloy. The resulting amalgam is temporarily viscous and formable so it can be packed into the tooth cavity. The amalgam sets quickly to a hard and wear-resistant restoration of the lost tooth structure.
It was common many years ago for a dentist or assistant to measure the individual amalgam components, and to mix the components manually immediately before packing into the cavity. This time-consuming and error-prone procedure (which involves handling of mercury) is replaced in modern dentistry by factory prepackaging of the isolated and precisely measured components in a multicompartment capsule or container. The capsule is manipulated to enable the components to flow together and mix when the capsule is inserted into a high-speed vibratory shaker or amalgamator. The capsule is then separated so the resulting amalgam can be dispensed.
Prior to the mixing procedure, it is essential that the mercury and silver components be completely isolated from each other by a barrier, but it is also desirable to have a quick and simple way of enabling the components to intermix completely when the capsule is shaken. In some capsule designs, the capsule is manipulated (e.g., by twisting of an end portion, or depression of a plunger) to puncture, sever or dislodge the barrier. Other designs are intended for automatic puncture or separation of the barrier by impact of a pestle (a rod or bar within one of the capsule compartments, and which aids the mixing process) during initial shaking of the capsule on an amalgamator. Summaries of typical such prior-art capsules are given in U.S. Pat. Nos. 4,182,447 and 4,552,266, and, for brevity, will not here be repeated.
The goal of good capsule design is to provide a leak-free multicompartment container which stores the components in complete isolation, and yet insures complete intermixing with as little handling as possible by the dentist or technician. Capsules which require twisting or plunger activation require extra handling and careful manipulation, and the interior separation-barrier parts tend to diminish the available mixing volume which should be large (with respect to the volume of the mercury and silver-alloy powder or pellet) to insure fast and thorough component mixing. So-called "automatic" capsules (having amalgamator-initiated barrier separation) have also proved to be unreliable, the most common problems being complete failure of barrier release or separation, or partial failure such as incomplete rupture or puncture of a constant-thickness barrier diaphragm which prevents proper component intermixing.
The capsule of this invention is a significant forward step in the design of multicompartment containers, and is an "automatic" design which need only be placed in a shaker or amalgamator for the desired mixing interval, and then removed and separated to dispense the amalgam. No premixing manipulation of the capsule is needed, and a novel internal barrier diaphragm is reliably and completely opened during initial capsule shaking to enable thorough component mixing in a large, unimpeded chamber.